Pulmonary fibrosis characterizes a heterogeneous group of incurable lung disorders with progressive, irreversible destruction of the lung architecture and disruption of gas exchange. The prototype of these diseases, idiopathic pulmonary fibrosis (IPF), has a median life expectancy of three years from diagnosis to death. Currently, no effective treatment is available for this disease. The first clue as to the molecular mechanism responsible for IPF emerged from the discovery by two groups, including our group, that a subset of pulmonary fibrosis is caused by mutations in the genes encoding the protein component (TERT) and the RNA component (TERC) of telomerase, a ribonucleoprotein enzyme that catalyzes the addition of hexameric nucleotide repeats to the ends of linear chromosomes. In our studies, all affected members with mutations in telomerase have evidence of shortened telomere lengths in circulating leukocytes. However, mutations in these genes comprise less than 15% of patients with the familial form of the disease and less than 3% of patients with the more common sporadic form of the disease. Here we will characterize the genetic etiology of pulmonary fibrosis in a large collection of familial and sporadic pulmonary fibrosis subjects. First, we will determine if telomere dysfunction and telomere shortening is a more generalized feature of familial and sporadic pulmonary fibrosis in subjects who do not have telomerase mutations, as our preliminary studies suggest. Second, we will determine if mutations in other genes involved in telomere maintenance contribute to PF in the subset of patients without coding mutations in telomerase. Third, we will map new genetic loci that cause pulmonary fibrosis in large kindreds where the disease fails to co-segregate with the genes known to cause lung scarring. These studies have the potential for breaking new conceptual grounds for determining the underlying molecular pathogenesis of pulmonary fibrosis. Our multi-pronged approaches offer the promise of providing new targets for therapeutic intervention for this lethal, age-associated lung disease.